For purposes of carrying out leveling and marking work indoors as well as outdoors, laser devices are known that generate punctiform and/or linear laser beams. The laser beams serve to show reference points or reference lines on walls, ceilings and floors. When it comes to such laser devices, a distinction is made between rotation lasers, which generate a linear laser beam by rotating a source of laser beams or a beam-deflecting lens system around an axis of rotation, and punctiform and/or linear lasers, which generate punctiform and/or linear laser beams by means of beam-forming lens systems such as cylindrical lenses and prisms.
In order to project a laser beam onto a wall at a certain height, the laser device has to be positioned at the appropriate height. Holders are generally known with which laser devices can be fastened to a wall, to a wall-mounted rail or a ceiling-mounted rail, to a pipe and/or to a magnetic structure, as well as holders in the form of tripods that can be positioned freestanding on a substrate. The height of the holders is adjusted manually by means of a crank or else by a motor.
The maximum permissible laser output is limited in the case of laser devices that can be used without protective equipment such as goggles. When leveling and marking work is performed outdoors, the permissible laser outputs often yield laser beams that are hardly or not at all visible. In order to improve the visibility of laser beams, laser receivers are held in the laser beam. Laser receivers, as handheld devices, are held by an operator directly in the laser beam or else they are attached to a telescopic or leveling rod. The known laser receivers comprise a detector unit, an evaluation unit as well as optical display devices and acoustic indication devices.
In order to set the holder at a desired height, which is designated as the target position, a laser beam is directed at a detector unit of the laser receiver. By means of an evaluation unit, the difference between the actual position of the laser beam and the target position is calculated and then displayed optically and/or indicated acoustically by the laser receiver. The operator controls the holder by means of an operating unit until the laser beam is located in the target position.
The optical display device comprises an LCD display on which the height difference of the laser beam with respect to the target position is displayed in the form of graphic symbols using distance arrows and a center bar, and/or as a numerical value. The distance arrows have several stages of increasing or decreasing width in order to display the height difference of the laser beam with respect to the target position. The distance arrows increase when the height difference of the laser beam with respect to the target position increases, and they decrease when the height difference decreases.
The acoustic indication device comprises a loudspeaker that emits three different acoustic signals. If the laser beam is at the target position, a continuous tone sounds at a constant tone frequency. If the detector unit detects the laser beam above the target position, an acoustic signal sounds at the tone frequency that is modulated with a scanning signal having a first scanning frequency fT1. If the detector unit detects the laser beam below the target position, an acoustic signal sounds at the tone frequency that is modulated with a scanning signal having a second scanning frequency fT2. The second scanning frequency fT2 is lower than the first scanning frequency fT1.